Classification and coding: the first step in designing manufacturing cells.

As engineers look to cellular manufacturing for tomorrow's foundry, a plan for designing cells for permanent mold facilities is given.

To compete in the global market, foundries must produce low-cost, superior quality products and deliver them to the customer on time. Successful firms will employ only lean and highly skilled multifunctional work forces. Contrary to the onetime notion of shop floor workers knowing only one skill throughout their lifetime with the foundry, each worker will be trained to handle a variety of jobs.

Designing and operating such production systems presents a challenge to many manufacturers, including the foundry industry. While several larger firms address these challenges by downsizing, it is not the key to surviving in the global market. In fact, reducing the work force may affect employee morale, thereby reducing productivity.

The key is to redesign or transform the existing factory into a new generation of computer-integrated manufacturing. This innovative manufacturing philosophy is flexible (can produce a variety of products) and integrates company operations from design, production and marketing to suppliers and customers using computers and modern management information methods.

Such a system must be energy efficient and environmentally friendly, resulting in less material waste and pollution, low inventories and short changeover time for each job. Furthermore, it must be able to produce pans in small lot sizes, with highly trained shop floor workers responsible for inspecting almost 100% of the parts.

Traditional sampling techniques in which a quality control engineer picks a few castings from a batch of finished parts, measures the dimensions and accepts or rejects the entire lot based on the sample's dimensions will no longer exist. In the future, the production floor worker will have total autonomy in producing top-quality products--he/she will make, inspect and send only good parts to the next production process.

Cellular Manufacturing

Much attention has been given recently to cellular manufacturing as a way to achieve tomorrow's manufacturing demands. A manufacturing cell is a collection of production machines arranged to produce part families, which are parts that share similar operation processes. By arranging the facility into cells, manufacturers can obtain higher efficiencies at lower labor costs. Permanent mold foundries are examples of operations that lend themselves to cellular design.

The question is: "How do we redesign or transform an existing foundry into this new generation of computer integrated manufacturing?" Do we invest a large sum of money to automate, computerize and robotize existing production processes? Or do we implement the just-in-time (JIT) philosophy into an existing inefficient factory?

Obviously, these are not the correct steps to follow. The solution can be summarized in 11 steps. These steps are a modified version of those outlined by J.T. Black in his book, The Design of the Factory with a Future. While this article addresses only the first two steps, an understanding of the entire process for designing manufacturing cells is needed. The 11 steps are:

1. Design a classification and coding system--Working with design, production and marketing personnel, all the main parameters for producing all parts within the foundry must be identified.

2. Form generic part families--Then, design manufacturing cells to fabricate the individual members within the part family using appropriate production data.

3. Rapid exchange of tooling and dies--Reduce or eliminate setup using quick tooling and die change techniques.

4. Integrate quality control--Incorporate quality control into all cell production machines and throughout the foundry to reduce casting defects. This is achieved by forming groups of workers to identify, analyze and solve problems in small teams. Integrating quality control into each production step within the cell means adding sensors to the equipment to detect if the process variables are changing in ways that will lead to failure in meeting part specifications.

5. Practice preventive maintenance--Because workers are empowered to shut down a cell/line if needed, they are also responsible for daily routine maintenance of each machine. Each worker must be trained and authorized to fix minor problems without help from the regular maintenance crew.

6. Decouple, balance and level--Continuously update each cell to minimize the idle time of the cell worker. If bottlenecks occur, increase the number of certain machines to reduce the cycle time of each cell. Known as decoupling, this results in workers not having to wait at any machine as they make the complete loop in the cell. In assembly cells, cell balancing (combining several work-stations into a single ones) permits equal job times at each.

Leveling consists of maintaining a uniform production schedule to permit steady flow of material between cells. Sudden changes in scheduling raise the "blood pressure" of workers because they must work longer hours at a faster rate to meet the schedule.

7. Link cells/kanban--Foundries should be operated by a combination of MRP (material requirements planning) and a kanban (or pull) system. Kanban is a management information system for dynamically controlling the production and inventory of parts. In kanban, the downstream cells pull parts from the upstream cells in the correct quantities and at the appropriate times, eliminating excessive inventory of parts between cells. Thus, kanban is the key to the successful implementation of JIT delivery.

MRP is a management information system for handling ordering and scheduling of dependent-demand items. Dependent-demand items are those used for producing finished products--such as raw materials, parts and subassemblies. Unlike a kanban system, MRP assumes a fixed setup for ordering items. However, it lacks the flexibility for dynamic production control of the factory floor. The hybrid MRP-kanban system permits such flexibility, with MRP used for macroscheduling, and kanban used for microscheduling and operational production control.

8. Integrate continuous improvement--management and workers periodically reduce the work-in-process inventory, thereby exposing and fixing quality problems on the shop floor. Thus, continuous improvement can be used as a tool to benchmark existing casting production methods. Also, the foundry must look for novel approaches to eliminate or reduce material waste. An example is a foundry that operates its cupola melting unit to eliminate emission of harmful gases to the atmosphere.

9. Build vendor programs--In the age of ISO 9000, raw material suppliers are treated as an extension of the foundry. Foundry personnel should regularly meet with the supplier's personnel to discuss technical matters, such as raw material, quality and process specifications. Technical experts should assist one another in improving production methods.

Also, the foundry maintains a close relationship with its own customers--those who buy the products. For similar products, customers will buy the one with the lowest cost, highest quality and prompt delivery. The challenge is for future factories to meet these requirements.

10. Automate--If manpower can be reduced, automate cell production equipment. An example is a worker who stands idly by an automated machine to serve as a watchman, or when he/she cannot do anything constructive manually while the machine is running. In this example, no manpower can be reduced.

11. Computerize--Use computer-controlled material handling devices to serve the cell or any process within the cell for the same reason as in Step 10.

Getting Started

Steps 1 and 2 deserve much attention. Step 1 requires the design of a classification and coding system that captures the main parameters for producing all castings within the foundry. Because an efficient classification and coding system is shared by all departments, designing such a system must be a team effort among design, production and marketing departments.

Step 2 requires that generic part families be formed from the classification and coding system obtained from Step 1 and the design of manufacturing cells to fabricate each member within the part family using appropriate production data.

For a foundry that already has a classification and coding system, it can easily be integrated with a CAD/CAM system. If the foundry receives a new order, it first codes the part. Using the code value, a search is initiated through the classification and coding database. If a casting with similar geometric shape and specifications is found, the old design is retrieved from the CAD/CAM database. This design is then modified to obtain the new one.

Constructing new CNC files for producing the new patterns is easy because CNC files of the old geometry are quickly updated to obtain the part program for the new geometry. Also, the particular cell to produce the new product, alloy type, gas level and other process and quality specifications can be quickly obtained from the classification and coding database. With this database capability, foundries can reduce the lead time to produce a new casting.

The importance of a well-designed classification and coding system to a foundry production facility cannot be overemphasized. When such a system is integrated with solidification modelers, production planning system modules (MRP), production control and scheduling system modules (manufacturing simulators) and others, not only can foundries determine in advance the market feasibility of a new product but also the design, economy and manufacturability of the product. Such an integrated system allows the foundry to:

* Determine the number and type of equipment required to fabricate a product or product mix daily.

* Determine daily the number of workers, the amount of raw materials and the optimum work-in-process inventory required for a given product or product mix. Excessive inventory and scrap are minimized, resulting in significant savings in energy and production costs.

* Provide a more efficient layout of the equipment on the production floor, resulting in better production control and reduced floor space. Reduced floor space in turn reduces material handling costs.

* Enable foundry production managers to ask daily questions such as: "How much excess component production could we forgo if we improve assembly quality and reduce scrap levels?"

Table 1. Selected Parameter and Code Values for X Casting

Parameter                                  Selection                    Code

Type of Casting Process                    Permanent Mold               1
Casting Machine Size and Maximum
Casing Size (Width by Height)              12 x 18 Rotary (10" x 14")   1
Alloy Aluminum                             1
Lowest Permissible Pouring Temperature     1224-1226F                   13
Highest Permissible Pouring Temperature    1248-1250F                   25
Lowest Permissible Gas Level               Level 1                      1
Highest Permissible Gas Level              Level 2                      2
First Type of Sand Core Process            No Sand Core                 0
Second Type of Sand Core Process           No Sand Core                 0
Filtered Crucible Process                  Filtered Crucible            1
Cleaning and San Core Removal Process      No Cleaning                  0
Gate Removal Process                       Slitting Saw (Circular)      3
First Type of Finishing Process            Hand Grinder                 3
Second Type of Finishing Process           No Finishing                 0
Third Type of Finishing Process            No Finishing                 0
Welding                                    No Arc Welding               0
Straightening                              No straightening             0
First Type of Machining Process            Drilling                     2
Second Type of Machining Process           Boring                       1
Third Type of Machining Process            No Machining                 0
Heat Treatment                             T-69                         2
Coating Process                            Anodizing                    1
Inspection and Testing                     Brinnell Hardness            1
Packaging                                  Bulk Pack                    1
Casting code value: 1-1-1-13-25-1-2-0-0-1-0-3-3-0-0-0-0-2-1-0-2-1-1.

* Allow design, production and marketing departments to conduct concurrently a feasibility study for designing and fabricating a new product in-house. For a new product, the foundry can determine if it is economically feasible to produce in-house, or if part of the product or the whole product should be subcontracted to others.

* Assist in benchmarking existing production methods (Step 8), thereby revealing bottlenecks on the production floor.

Unlike other metal processing industries such as machining, designing a cellular manufacturing system for the foundry industry is difficult because of the complexity of different parameters. Thus, a fundamental understanding of the classification and coding system for forming part families and manufacturing cells is important.

Classification and Coding

A classification and coding system is a method for sorting coded parts into part families based on the specific parameters of the parts. Using production data, the machines and workstations can then be classified into cells to produce the part families.

Classification involves arranging parts into groups by some scheme. The scheme brings parts together by virtue of their similarities. These assemblages are then separated by a specific difference. Coding is a collection of symbols that identifies the parameters needed for design and production of parts.

In any classification and coding system, identifying the appropriate parameters is the first step. Processes dictate cells and their layouts. Therefore, parameters must be designed to include information needed for part design and manufacturing. The University of Missouri-Rolla and Stahl Specialty Co., Kingsville, Missouri, have defined the most important parameters for designing the classification and coding system for a typical permanent mold factory. These parameters are listed in Fig. 1.

Using these parameters, the foundry can code the parts and then design the classification and coding system. The system must be flexible and easily adaptable to future technological changes.

An example of how the process develops for a particular casting is provided in Table 1. It identifies the key parameter, the selected parameter and its corresponding code of the casting. At the end of the table is the X casting's code value.

Also, the system can form part families and classify the production processes into cells for producing the part families. Software is being developed that streamlines the classification and coding process. The system is now being tested at Stahl. A brief description of how it works is given below:

1. The user makes the selections from pull-down menus to construct the group code for a casting to be produced.

2. All the castings produced by a permanent mold foundry are coded. As the castings are coded, the model automatically constructs the part families for the company.

3. The user selects a specific casting to be manufactured. The model automatically searches for the particular family to which the casting belongs.

4. The user can now choose the casting in question or any other casting within the family for the cell design.

5. The user enters the production data for producing the casting.

6. The model automatically determines the appropriate machines and correct number of each machine within the cell to fulfill the production requirements.

7. The model then displays all the machines on the computer screen.

8. The user can now design a cell layout for simulation analysis. Figure 2 shows an example of a cell constructed by the system, which is being tested at Stahl.

After the system has been successfully tested at Stahl, it will be revised for other foundries. If needed, new parameters will be defined. As time goes on, classification and coding systems will need to be modified to accommodate new technologies and process.

Later, a manufacturing simulator, production planning/management information system (MRP/MIS) modules and other software packages (such as CAD/CAM/CAE, rapid prototyping and casting design property database) will be interfaced with the model.

With the MIS module, the foundry can determine daily the optimum production costs such as inventory, labor and other costs. Thus, such an integrated system will permit a foundry to optimize the efficiency of its daily operations. Figure 3 shows how a new generation of computer integrated manufacturing incorporates other software modules for the foundry industry.

The results from a manufacturing simulator can assist the foundry manager in evaluating steps 3-11 before implementing them on the production floor. Thus, these steps are included as part of the capabilities of the simulator. Step 7 also is included in the MRP-II/MIS.

Fig. 1. Based on Stahl Specialty Co.'s experience, these are the most important parameters for designing the classification and coding system for a typical permanent mold foundry.

Type of casting process

Primary process

--Machine size and maximum casting size

Alloy type

Pouring temperature

--Lowest permissible pouring temperature

--Highest permissible pouring temperature

Gas level

--Lowest permissible gas level

--Highest permissible gas level

Core type

--First type of sand core process

--Second type of sand core process

Filtered crucible

Cleaning and sand core removal process

Gate removal process

Finishing process

--First type of finishing process

--Second type of finishing process

--Third type of finishing process

Straightening

Welding

Machining process

--First type of machining process

--Second type of machining process

--Third type of machining process

Heat treatment

Coating

Inspection and testing

Packaging